Tau PET Braak staging across the Alzheimer Disease continuum using Flortaucipir and MK6240

In 682 people spanning the aging-to-AD continuum, tau PET Braak staging agrees within tracers (89–92%) but is only moderately interchangeable across [18F]Flortaucipir vs [18F]MK6240 (43%, weighted kappa = 0.54).

• Why it matters: Cross-tracer differences matter because early-to-intermediate Braak stages (the therapeutic window) are where staging mismatch is most likely to affect trial enrollment and clinical stratification.
• What they did: In a prospective head-to-head comparison, tau PET Braak stages from [18F]Flortaucipir and [18F]MK6240 were directly compared, including stage-frequency benchmarking against an external neuropathological cohort (N = 4,422).
• The result: Cross-tracer agreement drops to 14–23% at early-to-intermediate stages, with [18F]MK6240 assigning higher stages in over 90% of discordant cases (about one Braak stage higher on average).

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